U.S. patent application number 09/912326 was filed with the patent office on 2002-03-14 for color cathode ray tube having plural electrostatic quadrupole lenses.
Invention is credited to Katou, Shinichi, Miyagawa, Kouichi, Noguchi, Kazunari, Uchida, Gou.
Application Number | 20020030430 09/912326 |
Document ID | / |
Family ID | 18759439 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020030430 |
Kind Code |
A1 |
Miyagawa, Kouichi ; et
al. |
March 14, 2002 |
Color cathode ray tube having plural electrostatic quadrupole
lenses
Abstract
A color cathode ray tube has a three in-line beam electron gun.
The electron gun includes a first group of focus electrodes
supplied with a first fixed focus voltage and a second group of
focus electrodes supplied with a second focus voltage comprised of
a fixed voltage and a dynamic voltage synchronized with beam
deflection. Plural axially spaced electrostatic quadrupole lenses
are formed between facing ones of the first and second groups of
focus electrodes. One of the plural electrostatic quadrupole lenses
nearest to the cathodes is configured so as to produce a lens
action weaker on two side electron beams than on the center
electron beam.
Inventors: |
Miyagawa, Kouichi; (Mobara,
JP) ; Katou, Shinichi; (Mobara, JP) ; Noguchi,
Kazunari; (Chiba, JP) ; Uchida, Gou; (Mobara,
JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
18759439 |
Appl. No.: |
09/912326 |
Filed: |
July 26, 2001 |
Current U.S.
Class: |
313/414 |
Current CPC
Class: |
H01J 29/503 20130101;
H01J 2229/4841 20130101 |
Class at
Publication: |
313/414 |
International
Class: |
H01J 029/50 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2000 |
JP |
2000-273513 |
Claims
What is claimed is:
1. A color cathode ray tube comprising an evacuated envelope
comprising a panel portion, a neck portion and a funnel portion for
connecting said panel portion and said neck portion, a phosphor
screen formed on an inner surface of said panel portion, an in-line
type electron gun housed in said neck portion, and an electron beam
deflection yoke mounted around a vicinity of a transitional region
between said neck portion and said funnel portion, said in-line
type electron gun comprising: an electron beam generating section
having three in-line cathodes, a first electrode serving as an
electron beam control electrode and a second electrode serving as
an accelerating electrode arranged in the order named for
projecting three electron beams arranged approximately in parallel
with each other in a horizontal plane toward said phosphor screen;
a first group of focus electrodes supplied with a first focus
voltage of a fixed value; a second group of focus electrodes
supplied with a second focus voltage comprised of a fixed voltage
and a dynamic voltage varying in synchronism with deflection of
said three electron beams; an anode forming a main lens in
cooperation with an adjacent one of said second group of focus
electrodes; and a plurality of axially spaced electrostatic
quadrupole lenses being formed between facing ones of said first
and second groups of focus electrodes such that each of said
plurality of electrostatic quadrupole lenses increases a lens
strength thereof for focusing said three electron beams in one of
horizontal and vertical directions, and increases a lens strength
thereof for diffusing said three electron beams in another of the
horizontal and vertical directions, with an increase in a focus
voltage difference between said first focus voltage and said second
focus voltage, wherein a first one of said plurality of
electrostatic quadrupole lenses disposed nearest to said three
in-line cathodes is configured so as to produce a lens action
weaker on two side electron beams of said three electron beams than
on a center electron beam of said three electron beams.
2. A color cathode ray tube according to claim 1, wherein said
first one of said plurality of electrostatic quadrupole lenses
increases a lens strength thereof for focusing said three electron
beams in one of horizontal and vertical directions, and increases a
lens strength thereof for diffusing said three electron beams in
another of the horizontal and vertical directions, with an increase
in a focus voltage difference between said first focus voltage and
said second focus voltage, and a second one of said plurality of
electrostatic quadrupole lenses located downstream from said first
one of said plurality of electrostatic quadrupole lenses increases
a lens strength thereof for focusing said three electron beams in
said another of horizontal and vertical directions, and increases a
lens strength thereof for diffusing said three electron beams in
said one of the horizontal and vertical directions, with the
increase in the focus voltage difference.
3. A color cathode ray tube according to claim 1, wherein said
first one of said plurality of electrostatic quadrupole lenses
comprises a center lens for said center electron beam and two side
lenses for said two electron beams, each of said center lens and
said two side lenses is formed between a respective one of three
vertically elongated apertures formed in one of said facing ones of
said first and second groups of focus electrodes and a
corresponding one of three horizontally elongated apertures formed
in another of said facing ones of said first and second groups of
focus electrodes, and ratios of a vertical diameter to a horizontal
diameter of generally rectangular portions of said vertically and
horizontally elongated apertures for said center electron beam
satisfy at least one of the following condition: (i) the ratio of
said vertically elongated aperture for said center electron beam is
greater than a ratio of a vertical diameter to a horizontal
diameter of respective generally rectangular portions of said
vertically elongated apertures for said two side electron beams,
and (ii) the ratio of said horizontally elongated aperture for said
center electron beam is smaller than a ratio of a vertical diameter
to a horizontal diameter of respective generally rectangular
portions of said horizontally elongated apertures for said two side
electron beams.
4. A color cathode ray tube according to claim 1, wherein said
first one of said plurality of electrostatic quadrupole lenses
comprises a center lens for said center electron beam and two side
lenses for said two electron beams, at least one of said facing
ones of said first and second groups of focus electrodes forming
said first one of said plurality of electrostatic quadrupole lenses
is formed with one of (i) three vertically elongated apertures and
(ii) three horizontally elongated apertures, and a ratio of a
vertical diameter to a horizontal diameter of a generally
rectangular portion of said center electron beam satisfies one of
the following condition: (iii) when said at least one of said
facing ones of said first and second groups of focus electrodes
forming said first one of said plurality of electrostatic
quadrupole lenses is formed with said three vertically elongated
apertures, the ratio of said vertically elongated aperture for said
center electron beam is greater than a ratio of a vertical diameter
to a horizontal diameter of respective generally rectangular
portions of said vertically elongated apertures for said two side
electron beams, and (iv) when said at least one of said facing ones
of said first and second groups of focus electrodes forming said
first one of said plurality of electrostatic quadrupole lenses is
formed with said three horizontally elongated apertures, the ratio
of said horizontally elongated aperture for said center electron
beam is smaller than a ratio of a vertical diameter to a horizontal
diameter of respective generally rectangular portions of said
horizontally elongated apertures for said two side electron
beams.
5. A color cathode ray tube according to claim 1, wherein said
first one of said plurality of electrostatic quadrupole lenses
comprises a center lens for said center electron beam and two side
lenses for said two electron beams, each of said center lens and
said two side lenses is formed by plates attached to at least one
of said facing ones of said first and second groups of focus
electrodes so as to sandwich a respective one of said three
electron beams therebetween, and a spacing between said plates
forming each of said two side lenses is greater than a spacing
between said plates forming said center lens in at least one of
horizontal and vertical directions.
6. A color cathode ray tube according to claim 2, wherein said
first one of said plurality of electrostatic quadrupole lenses
comprises a center lens for said center electron beam and two side
lenses for said two electron beams, each of said center lens and
said two side lenses is formed between a respective one of three
vertically elongated apertures formed in one of said facing ones of
said first and second groups of focus electrodes and a
corresponding one of three horizontally elongated apertures formed
in another of said facing ones of said first and second groups of
focus electrodes, and ratios of a vertical diameter to a horizontal
diameter of generally rectangular portions of said vertically and
horizontally elongated apertures for said center electron beam
satisfy at least one of the following condition: (i) the ratio of
said vertically elongated aperture for said center electron beam is
greater than a ratio of a vertical diameter to a horizontal
diameter of respective generally rectangular portions of said
vertically elongated apertures for said two side electron beams,
and (ii) the ratio of said horizontally elongated aperture for said
center electron beam is smaller than a ratio of a vertical diameter
to a horizontal diameter of respective generally rectangular
portions of said horizontally elongated apertures for said two side
electron beams.
7. A color cathode ray tube according to claim 2, wherein said
first one of said plurality of electrostatic quadrupole lenses
comprises a center lens for said center electron beam and two side
lenses for said two electron beams, at least one of said facing
ones of said first and second groups of focus electrodes forming
said first one of said plurality of electrostatic quadrupole lenses
is formed with one of (i) three vertically elongated apertures and
(ii) three horizontally elongated apertures, and a ratio of a
vertical diameter to a horizontal diameter of a generally
rectangular portion of said center electron beam satisfies one of
the following condition: (iii) when said at least one of said
facing ones of said first and second groups of focus electrodes
forming said first one of said plurality of electrostatic
quadrupole lenses is formed with said three vertically elongated
apertures, the ratio of said vertically elongated aperture for said
center electron beam is greater than a ratio of a vertical diameter
to a horizontal diameter of respective generally rectangular
portions of said vertically elongated apertures for said two side
electron beams, and (iv) when said at least one of said facing ones
of said first and second groups of focus electrodes forming said
first one of said plurality of electrostatic quadrupole lenses is
formed with said three horizontally elongated apertures, the ratio
of said horizontally elongated aperture for said center electron
beam is smaller than a ratio of a vertical diameter to a horizontal
diameter of respective generally rectangular portions of said
horizontally elongated apertures for said two side electron
beams.
8. A color cathode ray tube according to claim 2, wherein said
first one of said plurality of electrostatic quadrupole lenses
comprises a center lens for said center electron beam and two side
lenses for said two electron beams, each of said center lens and
said two side lenses is formed by plates attached to at least one
of said facing ones of said first and second groups of focus
electrodes so as to sandwich a respective one of said three
electron beams therebetween, and a spacing between said plates
forming each of said two side lenses is greater than a spacing
between said plates forming said center lens in at least one of
horizontal and vertical directions.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a cathode ray tube, and in
particular to a color cathode ray tube having an in-line type
electron gun employing a multistage focus lens for focusing a
plurality of electron beams on a phosphor screen.
[0002] Shadow mask type color cathode ray tubes are most commonly
used as TV picture tubes and monitor tubes for information
terminals. The shadow mask type color cathode ray tubes house an
electron gun for emitting a plurality (usually three) of electron
beams within one end of an evacuated envelope, a phosphor screen
formed of phosphors coated on an inner surface of the evacuated
envelope at the other end thereof for emitting light of a plurality
(usually three) of colors, and a shadow mask which serves as a
color selection electrode and is closely spaced from the phosphor
screen. The electron beams emitted from the electron gun are
deflected to scan the phosphor screen two-dimensionally by magnetic
fields generated by a deflection yoke mounted externally of the
evacuated envelope and to display a desired image on the phosphor
screen.
[0003] FIG. 8 is a cross-sectional view of the shadow mask type
color cathode ray tube for explaining its structural example,
reference numeral 81 denotes a panel portion forming a viewing
screen, 82 is a neck portion for housing an electron gun, 83 is a
funnel portion for connecting the panel portion 81 and the neck
portion 82, 84 is a phosphor screen, 85 is a shadow mask serving as
a color selection electrode, 86 is a mask frame for supporting the
shadow mask 85, 87 is a magnetic shield for shielding extraneous
magnetic fields such as the earth's magnetic field, 88 is a mask
suspension mechanism, 89 is an in-line type electron gun, reference
character DY denotes a deflection yoke, reference numeral 83a
denotes an internal conductive coating, 82a are stem pins, and
reference character GA denotes a getter.
[0004] In this the color cathode ray tube, the evacuated envelope
is comprised of the panel portion 81, the neck portion 82 and the
funnel portion 83, and electron beams B (one center electron beam
and two side electron beams, only one of which is shown) emitted
from the electron gun 89 housed in the neck portion 82 scan the
phosphor screen 84 in two dimensions by being subjected to the
horizontal and vertical deflection magnetic fields produced by the
deflection yoke DY.
[0005] The deflection yoke DY is of the self-converging type which
provides a pin cushion-like horizontal deflection magnetic field
and a barrel-like vertical deflection magnetic field to converge
the plural electron beams over the entire phosphor screen.
[0006] The electron beams B are modulated in amount by modulating
signals such as video signals supplied via the stem pins 82a, are
color-selected by the shadow mask 85 disposed immediately in front
of the phosphor screen 84, and impinge upon the phosphors of the
corresponding colors to reproduce a desired image.
[0007] The cathode ray tubes of this kind are provided with a
multistage focus lens in the electron gun and a so-called dynamic
focusing system is widely adopted where at least one of the
electrodes constituting the multistage focus lens is supplied with
a voltage varying dynamically, to obtain sufficiently small
electron beam spots over the entire phosphor screen.
[0008] FIG. 9 is a schematic cross-sectional view of an example of
an electrode structure of an in-line type electron gun employed in
a color cathode ray tube, taken perpendicular to the in-line
direction of three in-line electron beams.
[0009] In FIG. 9, reference numeral 91 denote three cathodes each
having a heater incorporated therein, 92 is a control electrode, 93
is an accelerating electrode, 95 is a focus electrode of a first
group, 94 and 96 are focus electrodes of a second group, 941, 951
and 952, and 961 are protuberant correction plates attached to the
focus electrodes 94, 95 and 96, respectively, 96b is a correction
plate electrode, 97 is an anode, 97a is an anode-side correction
electrode, and 98 is a shield cup.
[0010] The focus electrode 95 of the first group is supplied with a
fixed focus voltage Vf1, the focus electrodes 94, 96 of the second
group are supplied with a fixed voltage Vf2 superposed with a
dynamic voltage varying with the amount of deflection of the
electron beams, and the anode 97 is supplied with an anode voltage
Eb.
[0011] In the electron gun of this structure, a second-stage
electrostatic quadrupole lens LB is formed between the protuberant
correction plates 952 and the protuberant correction plates 961
attached to the focus electrode 95 of the first group and the focus
electrode 96 of the second group, respectively, and a first-stage
electrostatic quadrupole lens LA for shaping the electron beams is
formed between the protuberant correction plates 941 and the
protuberant correction plates 951 attached to the focus electrode
94 of the second group and the focus electrode 95 of the first
group, respectively. The first-stage electrostatic quadrupole lens
LA and the second-stage electrostatic quadrupole lens LB are
configured such that the first-stage electrostatic quadrupole lens
LA focuses the electron beams in one of the horizontal and vertical
directions and diffuses the electron beams in the other of the
horizontal and vertical directions, and on the other hand, the
second-stage electrostatic quadrupole lens LB diffuses the electron
beams in the one of the horizontal and vertical directions and
focuses the electron beams in the other of the horizontal and
vertical directions. A main lens LM is formed between the focus
electrode 96 of the second group and the anode 97.
[0012] The thermionic electrons emitted from the heated cathodes 91
are accelerated toward the control electrode 92 by a potential of
the accelerating electrode 93 to form three electron beams. After
passing through the electron beam apertures 92a in the control
electrode 92, the electron beam apertures 93a in the accelerating
electrode 93, and the focus electrodes 94-96, the three electron
beams are focused on the phosphor screen to form the beam spots by
the main lens LM formed between the focus electrode 96 of the
second group and the anode 97.
[0013] The electron guns used in color cathode ray tubes such as TV
picture tubes and display monitor tubes need to provide a good
focus over the entire phosphor screen area and high image
resolution. Consequently, the electron guns need to control the
cross-sectional shape of the electron beams properly according to
the amount of electron beam deflection.
[0014] With the above-described electron gun, the cross-sectional
shape of the electron beams entering the main lens is elongated
vertically with the increasing amount of deflection of the electron
beams by the astigmatism-correcting electrostatic quadrupole lens
LB formed between the focus electrodes 95 and 96. On the other
hand, the electron beams are greatly influenced by deflection
defocusing which originates in the deflection yoke, compresses the
vertical diameter of the cross section of the electron beams,
expands the horizontal diameter of the cross section of the
electron beams, and thereby elongates the cross section of the
electron beams horizontally. Consequently, the electron beam spots
are elongated horizontally at the periphery of the viewing
screen.
[0015] When the electron beam spots on the phosphor screen becomes
horizontally elongated, moire occurs easily due to interference
between the scanning lines of the electron beams and the
arrangement of electron beam aperture in the shadow mask. If moire
appears in the viewing screen, it is difficult to obtain good and
uniform focus over the entire screen area, and to recognize
characters and images displayed on the viewing screen, and
consequently, substantial image resolution is degraded.
[0016] Therefore it is necessary to control the shape of the
electron beam spot with the amount of beam deflection by forming,
in addition to the above electrostatic quadrupole lens LB, another
electrostatic quadrupole lens LA serving as an electron beam
shaping lens between the focus electrodes 94 and 95 in a position
nearer to the cathodes 91 than the electrostatic quadrupole lens LB
is.
[0017] The beam-shaping electrostatic quadrupole lens LA is capable
of shaping the electron beam spots with the amount of deflection of
the electron beams as desired, and consequently, is capable of
canceling elongation of the electron beam spots at the screen
periphery caused by the astigmatism-correcting electrostatic
quadrupole lens LB. Occurrence of moire is suppressed such that
good and uniform focus is obtained over the entire screen. The
electron gun employing the above-explained electrostatic quadrupole
lenses are disclosed in Japanese Patent Application Laid-open No.
Hei 8-31332 (laid-open on Feb. 2, 1996), for example.
SUMMARY OF THE INVENTION
[0018] In the above-described in-line type electron gun, deflection
defocusing produced by the self-converging magnetic fields of the
deflection yoke makes different changes in cross-sectional shape
among a green electron beam (hereinafter the G beam) emitted from a
center electron gun, a red electron beam (hereinafter the R beam)
emitted from one of the two side electron guns, and a blue electron
beam (hereinafter the B beam) emitted from the other of the two
side electron guns.
[0019] Now consider a case in which the red electron gun is on the
right-hand side, the green electron gun is on the tube axis, and
the blue electron gun is on the left-hand side as seen from
phosphor screen. When the R beam is deflected to the left-hand side
of the screen or the B beam is deflected to right-hand side of the
screen, the R beam or the B beam is subjected to weaker influence
of the deflection defocusing produced by the deflection yoke than
the G beam is, and consequently, the beam spot of the R beam or the
B beam is horizontally elongated less than the G beam, and
therefore the vertical diameter of the R beam at the left-hand side
of the screen and that of the B beam at the right-hand side of the
screen are larger than the vertical diameter of the G beam.
[0020] The current of the R beam is 1.1 to 1.3 times the current of
the G beam when a white scene is displayed on the viewing screen.
Therefore, when the color temperature is adjusted for the display
monitor, the spot diameter of the R beam becomes larger than that
of the G beam such that the spot diameter of the R beam is
increased further at the left-hand side of the screen. As a result,
the R beam at the left-hand side of the screen and the B beam at
the right-hand side of the screen are overcompensated to provide
vertically elongated beam spots by the beam-shaping electrostatic
quadrupole lens LA, the vertical resolution is deteriorated, and
this makes it difficult to obtain good and uniform characteristics
over the entire screen area, which is one of the problems to be
solved.
[0021] It is a representative object of the present invention to
provide a high-resolution color cathode ray tube by shaping the
beam spots into a good shape over a wide area of the viewing
screen, and thereby suppressing occurrence of moire.
[0022] To achieve the above object, in a representative aspect of
the present invention, plural electrostatic quadrupole lenses are
disposed in spaced relationship in the in-line type electron gun,
and one of the electrostatic quadrupole lens disposed nearest to
the cathodes is configured so as to produce a lens action weaker on
the two side electron beams of the three electron beams than on the
center electron beam of the three electron beams.
[0023] In accordance with an embodiment of the present invention,
there is provided a color cathode ray tube comprising an evacuated
envelope comprising a panel portion, a neck portion and a funnel
portion for connecting the panel portion and the neck portion, a
phosphor screen formed on an inner surface of the panel portion, an
in-line type electron gun housed in the neck portion, and an
electron beam deflection yoke mounted around a vicinity of a
transitional region between the neck portion and the funnel
portion, the in-line type electron gun comprising: an electron beam
generating section having three in-line cathodes, a first electrode
serving as an electron beam control electrode and a second
electrode serving as an accelerating electrode arranged in the
order named for projecting three electron beams arranged
approximately in parallel with each other in a horizontal plane
toward the phosphor screen; a first group of focus electrodes
supplied with a first focus voltage of a fixed value; a second
group of focus electrodes supplied with a second focus voltage
comprised of a fixed voltage and a dynamic voltage varying in
synchronism with deflection of the three electron beams; an anode
forming a main lens in cooperation with an adjacent one of the
second group of focus electrodes; and a plurality of axially spaced
electrostatic quadrupole lenses being formed between facing ones of
the first and second groups of focus electrodes such that each of
the plurality of electrostatic quadrupole lenses increases a lens
strength thereof for focusing the three electron beams in one of
horizontal and vertical directions, and increases a lens strength
thereof for diffusing the three electron beams in another of the
horizontal and vertical directions, with an increase in a focus
voltage difference between the first focus voltage and the second
focus voltage, wherein a first one of the plurality of
electrostatic quadrupole lenses nearest to the three in-line
cathodes is configured so as to produce a lens action weaker on two
side electron beams of the three electron beams than on a center
electron beam of the three electron beams.
[0024] The present invention is not limited to the above structures
or the structures of the embodiments described subsequently, and
various changes and modifications may be made without departing
from the scope of the invention as defined in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] In the accompanying drawings, in which like reference
numerals designate similar components throughout the figures, and
in which:
[0026] FIG. 1 is a schematic cross-sectional view of an electron
gun for explaining a color cathode ray tube in accordance with an
embodiment of the present invention;
[0027] FIGS. 2A and 2B are plan views of the focus electrodes of
the electron gun of FIG. 1, taken in the directions of the arrows
IIA-IIA and IIB-IIB of FIG. 1, respectively;
[0028] FIG. 3 is a schematic cross-sectional view of an electron
gun for explaining a color cathode ray tube in accordance with
another embodiment of the present invention;
[0029] FIG. 4 is a perspective view of major portions of the focus
electrodes of FIG. 3;
[0030] FIG. 5 is a schematic cross-sectional view of an electron
gun for explaining a color cathode ray tube in accordance with
still another embodiment of the present invention;
[0031] FIG. 6 is a perspective view similar to that of FIG. 4,
illustrating major portions of focus electrodes for explaining a
color cathode ray tube in accordance with still another embodiment
of the present invention;
[0032] FIG. 7 is a perspective view similar to that of FIG. 4,
illustrating major portions of focus electrodes for explaining a
color cathode ray tube in accordance with still another embodiment
of the present invention;
[0033] FIG. 8 is a cross-sectional view of an example of a shadow
mask type color cathode ray tube; and
[0034] FIG. 9 is a schematic cross-sectional view of an example of
an electrode configuration of an in-line type electron gun used in
a color cathode ray tube.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The detailed explanation will be given to the embodiments
according to the present invention referring to the drawings.
[0036] FIG. 1 is a schematic cross-sectional view of an electron
gun viewed in a direction perpendicular to the in-line direction of
the three in-line electron beams for explaining a first embodiment
of a color cathode ray tube according to the present invention. The
same reference numerals as utilized in FIG. 9 designate
functionally similar portions in FIG. 1.
[0037] In this embodiment, an electron beam generating section
comprises cathodes 1, a control electrode 2 and an accelerating
electrode 3, and an electron beam focusing section comprises a
third electrode 41 of a first focus electrode group and a third
electrode of a second focus electrode group which constitute a
third electrode 4, a fourth electrode 5, a fifth electrode 61 of
the first focus electrode group and a fifth electrode 62 of the
second focus electrode group which constitute a fifth electrode 6,
an anode 7, a shield cup 8, a correction plate electrode 63
disposed within the fifth electrode 62 of the second focus
electrode group, and a correction plate electrode 71 disposed
within the anode 7. Reference numerals 2a, 3a, 41a, 42a and 42b
denote electron beam apertures in the electrodes.
[0038] In the above electrode configuration, the accelerating
electrode 3 and the fourth electrode 5 are supplied with a fixed
voltage Ec2 of about 400V to about 1000V, and the third electrode
41 and the fifth electrode 61 of the first focus electrode group
are supplied with a first focus voltage of a fixed value Vf1. The
third electrode 42 and the fifth electrode 62 of the second focus
electrode group are supplied with a second focus voltage (Vf2+dVf)
which is a fixed voltage Vf2 superposed with a dynamic voltage dVf
varying with deflection angle of the electron beams scanning the
viewing screen. The first focus voltage is the fixed voltage Vf1 in
a range of 5 kV to 10 kV, for example, and the second focus voltage
is the fixed voltage Vf2 of 5 kV to 10 kv superposed with the
dynamic voltage dvf of 300 V to 1000 V varying with deflection
angle of the electron beams scanning the viewing screen, for
example.
[0039] Formed between the third electrode 41 of the first focus
electrode group and the third electrode 42 of the second focus
electrode group is a beam-shaping electrostatic quadrupole lens LA
for changing the cross-sectional shape of the electron beams with
increase in the dynamic voltage dvf. Formed between the fifth
electrode 61 of the first focus electrode group and the fifth
electrode 62 of the second focus electrode group is an astigmatism
producing electrostatic quadrupole lens LB for elongating the
cross-sectional shape of the electron beams vertically increasingly
with the increase in the dynamic voltage dvf. That is to say, in
this electron gun, the first-stage electrostatic quadrupole lens LA
nearer to the cathodes 1 and the second-stage electrostatic
quadrupole lens LB nearer to the anode 7 are spaced by a specified
distance from each other.
[0040] In the electrostatic quadrupole lens LA, opposing surfaces
of the third electrode 41 of the first focus electrode group and
the third electrode 42 of the second focus electrode group are
formed with horizontally elongated keyhole beam apertures 41a and
vertically elongated keyhole beam apertures 42a, respectively, as
described subsequently in greater detail in connection with FIGS.
2A and 2B. Formed between the third electrode 41 of the first focus
electrode group and the third electrode 42 of the second focus
electrode group is the electron beam-shaping electrostatic
quadrupole lens LA which serves to elongate horizontally the
cross-sectional shape of the electron beams with increase in the
dynamic voltage dVf. Further, the horizontally elongated keyhole
beam apertures formed in the third electrode 41 of the first focus
electrode group are configured such that the ratio of the vertical
diameter to the horizontal diameter of a rectangular portion of the
center beam aperture is smaller than that of a rectangular portion
of the respective side beam apertures, and the vertically elongated
keyhole beam apertures formed in the third electrode 42 of the
second focus electrode group are configured such that the ratio of
the vertical diameter to the horizontal diameter of a rectangular
portion of the center beam aperture is greater than that of a
rectangular portion of the respective side beam apertures, so that
the lens strength for the respective side beams is made weaker than
that for the center beam.
[0041] FIGS. 2A and 2B are plan views of major portions of the
third electrode 41 of the first focus electrode group and the third
electrode 42 of the second focus electrode group show in FIG. 1,
respectively. FIG. 2A is an illustration of the electron beam
apertures 41a formed in an end of the third electrode 41 of the
first focus electrode group facing the third electrode 42 of the
second focus electrode group, and FIG. 2B is an illustration of the
electron beam apertures 42a formed in an end of the third electrode
42 of the second focus electrode group facing the third electrode
41 of the first focus electrode group.
[0042] In FIG. 2A, the three electron beam apertures 41a in the
third electrode 41 of the first focus electrode group are made in
the form of the horizontally elongated keyhole having a vertical
diameter H. The horizontal diameter C1 of a rectangular portion of
the center electron beam aperture 41ac of the three electron beam
apertures 41a is made larger than the horizontal diameter S1 of a
rectangular portion of the side electron beam apertures 41as so
that the ratio H/C1 of the vertical diameter to the horizontal
diameter of the rectangular portion of the center electron beam
aperture 41ac is made smaller than the ratio H/S1 of the vertical
diameter to the horizontal diameter of the rectangular portion of
the side electron beam apertures 41as, and thereby the lens
strength of the electrostatic quadrupole lens for the side beams is
made weaker than that of the electrostatic quadrupole lens for the
center beam.
[0043] In FIG. 2B, the three electron beam apertures 42a in the
third electrode 42 of the second focus electrode group are made in
the form of the vertically elongated keyhole having a horizontal
diameter W. The vertical diameter C2 of a rectangular portion of
the center electron beam aperture 42ac of the three electron beam
apertures 42a is made larger than the vertical diameter S2 of a
rectangular portion of the side electron beam apertures 42as so
that the ratio C2/W of the vertical diameter to the horizontal
diameter of the rectangular portion of the center electron beam
aperture 42ac is made greater than the ratio S2/W of the vertical
diameter to the horizontal diameter of the rectangular portion of
the side electron beam apertures 42as, and thereby the lens
strength of the electrostatic quadrupole lens for the side beams is
made weaker than that of the electrostatic quadrupole lens for the
center beam in this third electrode 42 also.
[0044] In the above embodiment, the following two configurations
are employed:
[0045] (1) the ratio H/C1 of the vertical diameter to the
horizontal diameter of the rectangular portion of the center
electron beam aperture 41ac is made smaller than the ratio H/S1 of
the vertical diameter to the horizontal diameter of the rectangular
portion of the side electron beam apertures 41as in the third
electrode 41 of the first focus electrode group, and
[0046] (2) the ratio C2/W of the vertical diameter to the
horizontal diameter of the rectangular portion of the center
electron beam aperture 42ac is made greater than the ratio S2/W of
the vertical diameter to the horizontal diameter of the rectangular
portion of the side electron beam apertures 42as in the third
electrode 42 of the second focus electrode group.
[0047] However, the advantages similar to those obtained by the
above embodiment can be provided even if only one of the above two
configurations are employed.
[0048] The second-stage electrostatic quadrupole lens LB is formed
by a combination of four protuberant vertical correction plates 611
attached to the fifth electrode 61 of the first focus electrode
group and two protuberant horizontal correction plates 621 attached
to the fifth electrode 62 of the second focus electrode group. The
four protuberant vertical correction plates 611 protrude axially
from the fifth electrode 61 toward the fifth electrode 62 of the
second focus electrode group, and are arranged at equal intervals
in a direction of an in-line arrangement of the three electron
beams so as to shield the three adjacent electron beams from each
other. The two protuberant horizontal correction plates 62 protrude
axially from the fifth electrode 62 toward the fifth electrode 61
and are arranged approximately in parallel with the direction of
travel of the electron beams so as to sandwich the three electron
beams vertically.
[0049] In this embodiment, the beam-shaping electrostatic
quadrupole lens LA reduces the amount of correction for the R beam,
one of the two side electron beams, deflected to the left-hand side
of the viewing screen and the amount of correction for the B beam,
the other of the two side electron beams, deflected to the
right-hand side of the viewing screen, and consequently,
deterioration in resolution due to excessive increase in vertical
diameters of the beam spots can be suppressed.
[0050] On the other hand, the diameters of the beam spot formed by
the R beam deflected to the right-hand side of the screen and the
beam spot formed by the B beam deflected to the left-hand side of
the screen are elongated horizontally more than those of the beam
spots formed by the G beam which is the center electron beam, the R
beam deflected to the left-hand side of the screen, and the B beam
deflected to the right-hand side of the screen because the R beam
deflected to the right-hand side of the screen and the B beam
deflected to the left-hand side of the screen are strongly
influenced by the self-converging magnetic fields of the deflection
yoke. Further, the beam-shaping electrostatic quadrupole lens LA of
the above configuration provides weaker lens action on the R and B
beams than on the G beam, therefore the R and B beams are not
shaped as much as the G beam, and as a result the beam spots of the
R beam deflected to the right-hand side of the screen and the B
beam deflected to the left-hand side of the screen are elongated
horizontally after shaping by the beam-shaping electrostatic
quadrupole lens LA.
[0051] Generally, considering the proportion of brightness produced
by the G beam in a white scene, the brightness by the G beam
account for 70% to 80%. The G beam is dominant in occurrence of
moire, and consequently, even if the amount of correction of
elongation of the R and B beam spots due to the self-converging
magnetic fields of the deflection yoke is smaller than that of the
G beam, substantial deterioration in resolution is not caused by
moire.
[0052] Resolution in a single color by the R or B beam is of
practical importance among characteristics of a color cathode ray
tube, and vertical resolution is important especially for
displaying characters on the viewing screen. Therefore
characteristics of the color cathode ray tube are not degraded by
horizontal elongation of the spots of the R beam at the right-hand
side of the screen and the B beam at the left-hand side of the
screen which is produced by making the lens strength of the
beam-shaping electrostatic quadrupole lens LA for the R and B beams
weaker than that for the G beam.
[0053] As explained above, deterioration in resolution by the R and
B beams due to the self-converging magnetic fields of the
deflection yoke is suppressed by making the lens strength of the
beam-shaping electrostatic quadrupole lens LA for the R and B
beams, the two side beams, weaker than that for the G beam, the
center beam, and thereby realized are the G beam spot uniform over
the entire screen area, reduction of moire, and improvement of
resolution by the R and B beams.
[0054] FIG. 3 is a schematic cross-sectional view of an electron
gun for explaining a color cathode ray tube in accordance with
another embodiment of the present invention, viewed in a direction
of an in-line arrangement of the three electron beams. The same
reference numerals as utilized in FIGS. 1, 2, 8 and 9 designate
functionally similar portions in FIG. 3.
[0055] In the embodiment shown in FIG. 3, the fifth electrode 6 is
formed of the fifth electrode 65 of the first focus electrode
group, and the fifth electrodes 62 and 64 of the second focus
electrode group with the fifth electrode 65 interposed
therebetween.
[0056] The first-stage electrostatic quadrupole lens LA for beam
shaping is formed by four protuberant vertical correction plates
641 attached to the fifth electrode 64 of the second focus
electrode group and two protuberant horizontal correction plates
651 attached to the fifth electrode 65 of the first focus electrode
group. The four protuberant vertical correction plates 641 protrude
axially from the fifth electrode 64 toward the fifth electrode 65
of the first focus electrode group, and are arranged at specified
intervals in a direction of an in-line arrangement of the three
electron beams so as to shield the three adjacent electron beams
from each other. The two protuberant horizontal correction plates
651 protrudes axially from the fifth electrode 65 toward the fifth
electrode 64 and are arranged approximately in parallel with the
direction of travel of the electron beams so as to sandwich the
three electron beams vertically. The configurations of the
protuberant vertical correction plates 641 and the protuberant
horizontal correction plates 651 will be shown in FIG. 4 described
subsequently.
[0057] The second-stage electrostatic quadrupole lens LB is formed
by four protuberant vertical correction plates 652 attached to the
fifth electrode 65 of the first focus electrode group and two
protuberant horizontal correction plates 621 attached to the fifth
electrode 62 of the second focus electrode group. The four
protuberant vertical correction plates 652 protrude axially from
the fifth electrode 65 toward the fifth electrode 62 of the second
focus electrode group, and are arranged at equal intervals in a
direction of an in-line arrangement of the three electron beams so
as to shield the three adjacent electron beams from each other. The
two protuberant horizontal correction plates 621 protrude axially
from the fifth electrode 62 toward the fifth electrode 65 and are
arranged approximately in parallel with the direction of travel of
the electron beams so as to sandwich the three electron beams
vertically. The configurations of the protuberant vertical
correction plates 641 and the protuberant horizontal correction
plates 651 will be shown in FIG. 4 described subsequently.
[0058] The accelerating electrode 3 and the fourth electrode 5 are
supplied with a fixed voltage Ec2 of about 400V to about 1000V, and
the third electrode 43 and the fifth electrode 65 of the first
focus electrode group are supplied with a first focus voltage of a
fixed value Vf1. The fifth electrode 64 and the fifth electrode 62
of the second focus electrode group are supplied with a second
focus voltage (Vf2+dVf) which is a fixed voltage Vf2 superposed
with a dynamic voltage dvf varying with deflection angle of the
electron beams scanning the viewing screen. The first focus voltage
is the fixed voltage Vf1 in a range of 5 kV to 10 kV, for example,
and the second focus voltage is the fixed voltage Vf2 of 5 kV to 10
kV superposed with the dynamic voltage dVf of 300 V to 1000 V
varying with deflection angle of the electron beams scanning the
viewing screen, for example.
[0059] FIG. 4 is a perspective view of major portions of the
first-stage electrostatic quadrupole lens LA formed by the fifth
electrode 65 of the first focus electrode group and the fifth
electrode 64 of the second focus electrode group shown in FIG. 3.
In FIG. 4, the four protuberant vertical correction plates 641
attached to the fifth electrode 64 comprise a pair of inner
protuberant vertical correction plates 641c sandwiching the center
electron beam path horizontally and a pair of outer protuberant
vertical correction plates 641s located outside the respective side
beam paths in parallel with the inner protuberant vertical
correction plates 641c. The spacing WS1 between the outer
protuberant vertical correction plates 641s and the adjacent inner
protuberant vertical correction plates 641c is selected to be
greater than the spacing WC1 between the two inner protuberant
vertical correction plates 641c. The axial length L1 and the height
H1 are selected to be identical for all the four protuberant
vertical correction plates 641, in this embodiment. The fifth
electrode 65 of the first focus electrode group facing the fifth
electrode 64 is provided with two protuberant horizontal correction
plates 651 protruding toward the fifth electrode 64 sandwiching the
three electron beams vertically. The axial length L2 of the two
protuberant horizontal correction plates 651 and the spacing H2
between the two protuberant horizontal correction plates 651 are
selected to be greater than the axial length L1 and the height H1
of the four protuberant vertical correction plates 641,
respectively, and the width W2 of the protuberant horizontal
correction plates 651 is selected to be so sufficient as to
surround the three electron beam paths in cooperation with the four
protuberant vertical correction plates 641.
[0060] On the other hand, the second-stage electrostatic quadrupole
lens LB is formed by four protuberant vertical correction plates
652 attached to the fifth electrode 65 and two protuberant
horizontal correction plates 621 attached to the fifth electrode 62
facing the fifth electrode 65. The four protuberant vertical
correction plates 652 are of the same axial length and the height
and are arranged at equal intervals, and the two protuberant
horizontal correction plates 621 are of the same axial length and
the same width.
[0061] In this embodiment, the first-stage electrostatic quadrupole
lens LA for beam-shaping is capable of making its lens strength for
the side electron beams weaker than its lens strength for the
center electron beam, and provides good and uniform focus over the
entire viewing screen area as in the case of the first embodiment
described previously.
[0062] In the embodiment explained in connection with FIG. 4 the
four protuberant vertical correction plates 641 are of the same
axial length L1 and the height H1, but if the height and the axial
length of the outer protuberant vertical correction plates 641s are
selected to be smaller than the height and the axial length of the
inner protuberant vertical correction plates 641c, respectively,
and at the same time the spacing WS1 is selected to be greater than
the spacing WC1 as in the embodiment shown in FIG. 4, the lens
strength of the electrostatic quadrupole lens for the side electron
beams can be made even weaker than that for the center electron
beam.
[0063] FIG. 5 is a schematic cross-sectional view of an electron
gun for explaining a color cathode ray tube in accordance with
still another embodiment of the present invention viewed in the
direction of the in-line arrangement of the three electron beams.
The same reference numerals as utilized in FIGS. 1-4, 8 and 9
designate functionally similar portions in 5.
[0064] In the embodiment shown in FIG. 5, the first-stage
electrostatic quadrupole lens LA for beam shaping is formed by four
protuberant vertical correction plates 441 attached to the third
electrode 44 of the first focus electrode group and the two
protuberant horizontal correction plates 451 attached to the third
electrode 45 of the second focus electrode group facing the third
electrode 44. The four protuberant vertical correction plates 441
protrude axially from the third electrode 44 toward the third
electrode 45 of the second focus electrode group, and are arranged
at specified intervals in the direction of the in-line arrangement
of the three electron beams so as to shield the three adjacent
electron beams from each other. The two protuberant horizontal
correction plates 451 protrude axially from the third electrode 45
toward the third electrode 44 and are arranged approximately in
parallel with the direction of travel of the electron beams so as
to sandwich the three electron beams vertically. The spacing
between the two adjacent protuberant vertical correction plates 441
on opposite sides of the side electron beam path is selected to be
greater than the spacing between the two adjacent protuberant
vertical correction plates 441 on opposite sides of the center
electron beam path so that the lens strength of the electrostatic
quadrupole lens for the side electron beams is made weaker than
that for the center electron beam.
[0065] The second-stage electrostatic quadrupole lens LB is formed
by four protuberant vertical correction plates 671 attached to the
fifth electrode 67 of the second focus electrode group and two
protuberant horizontal correction plates 661 attached to the fifth
electrode 66 of the first focus electrode group facing the fifth
electrode 67. The four protuberant vertical correction plates 671
protrude axially from the fifth electrode 67 toward the fifth
electrode 66 of the first focus electrode group, and are arranged
at equal intervals in the direction of the in-line arrangement of
the three electron beams so as to shield the three adjacent
electron beams from each other. The two protuberant horizontal
correction plates 661 protrude axially from the fifth electrode 66
toward the fifth electrode 67 and are arranged approximately in
parallel with the direction of travel of the electron beams so as
to sandwich the three electron beams vertically. Reference numeral
67a denotes a correction plate electrode disposed within the fifth
electrode 67.
[0066] The accelerating electrode 3 and the fourth electrode 5 are
supplied with a fixed voltage Ec2 of about 400V to about 1000V, and
the third electrode 44 and the fifth electrode 66 of the first
focus electrode group are supplied with a first focus voltage of a
fixed value Vf1. The third electrode 45 and the fifth electrode 67
of the second focus electrode group are supplied with a second
focus voltage (Vf2+dVf) which is a fixed voltage Vf2 superposed
with a dynamic voltage dvf varying with deflection angle of the
electron beams scanning the viewing screen. The first focus voltage
is the fixed voltage Vf1 in a range of 5 kV to 10 kV, for example,
and the second focus voltage is the fixed voltage Vf2 of 5 kV to 10
kV superposed with the dynamic voltage dvf of 300 V to 1000 V
varying with deflection angle of the electron beams scanning the
viewing screen, for example.
[0067] FIG. 6 is a perspective view similar to that of FIG. 4,
illustrating major portions of focus electrodes for explaining a
color cathode ray tube in accordance with still another embodiment
of the present invention.
[0068] In the embodiment shown in FIG. 6, the first-stage
electrostatic quadrupole lens LA for beam shaping is formed by a
focus electrode 68 in the form of a plate and a focus electrode 69
comprised of three U-shaped electrodes. The focus electrode 69 is
formed of a generally U-shaped electrode 69c associated with the
center electron beam and two generally U-shaped electrodes 69s
associated with the two side electron beams, and the following
relationships are satisfied:
Wc2<Ws2, H3c>H3s, and L3c>L3s,
[0069] where Wc2=a spacing between two protuberant vertical
correction plates 691c of the electrode 69c associated with the
center electron beam,
[0070] H3c=a height of the protuberant vertical correction plates
691c,
[0071] L3c=an axial length of the protuberant vertical correction
plates 691c,
[0072] Ws2=a spacing between two protuberant vertical correction
plates 691s of the electrode 69s associated with the side electron
beams,
[0073] H3s=a height of the protuberant vertical correction plates
691s,
[0074] L3s=an axial length of the protuberant vertical correction
plates 691s.
[0075] FIG. 7 is a perspective view similar to that of FIG. 4,
illustrating major portions of focus electrodes for explaining a
color cathode ray tube in accordance with still another embodiment
of the present invention.
[0076] In the embodiment shown in FIG. 7, the first-stage
electrostatic quadrupole lens LA for beam shaping is formed by a
focus electrode 70 in the form of a plate and a generally U-shaped
focus electrode 71. The focus electrode 70 is formed with
vertically elongated keyhole beam apertures 70c and 70s, and the
vertical diameter c3 of the center beam aperture 70c is selected to
be larger than the vertical diameter s3 of the side beam apertures
70s. The generally U-shaped focus electrode 71 facing the focus
electrode 70 is formed with three circular beam apertures 71c, 71s
of the same diameter.
[0077] In this embodiment, the lens strength of the electrostatic
quadrupole lens for the side electron beams is be made weaker than
that for the center electron beam by making the vertical diameter
c3 of the center beam aperture 70c larger than the vertical
diameter s3 of the side beam apertures 70s. As explained above,
with the representative configurations of the present invention, by
making the lens strength of the beam-shaping electrostatic
quadrupole lens of the electron gun for the side electron beams
weaker than that for the center electron beam, there is provided a
cathode ray tube superior in resolution characteristics which has
suppressed deterioration in resolution of the side electron beams
caused by self-converging magnetic fields of the deflection yoke
and thereby provides good focus in a wide area of the viewing
screen and suppressed occurrence of moire.
* * * * *